Polyisocyanate compositions as with melamine-based curing agents are widely used as thermally crosslinkable curing agents for baking finishes. In recent years, it is pointed out that formalin is produced when a melamine-based curing agent is used, and polyisocyanates that are blocked with a blocking agent (blocked polyisocyanates) attract attention from the viewpoint of global environment, safety, health, and the like.
To date, oximes, phenols, alcohols, and lactams are known as blocking agents of blocked polyisocyanates.
A pyrazole-based blocked polyisocyanate composition (see, for example, Patent Literature 1) and an aliphatic secondary amine-based blocked polyisocyanate composition (see, for example, Patent Literature 2) are disclosed as blocked polyisocyanates capable of forming crosslinked coating films at relatively low temperatures.
A blocked polyisocyanate composition having a malonic acid diester as a blocking agent (see, for example, Patent Literature 3), blocked polyisocyanate compositions having diethyl malonate and ethyl acetoacetate as blocking agents (see, for example, Patent Literatures 4 and 5), and the like are proposed as blocked polyisocyanate compositions enabling the baking temperature to be further lowered.